proof-of-existence

Proof of Existence Pallet

This tutorial illustrates how to create a custom pallet for a Substrate runtime using macros that are part of the FRAME development environment.

For this tutorial, you'll build a simple proof-of-existence application. Proof-of-existence is an approach to validating the authenticity and ownership of a digital object by storing information about the object on the blockchain. Because the blockchain associates a timestamp and account with the object, the blockchain record can be used to "prove" that a particular object existed at a specific date and time. It can also verify who the owner of a record was at that date and time.

Digital objects and hashes

Instead of storing an entire file on the blockchain, it can be much more efficient to simply store a cryptographic hash of that file. This is also known as a "digital fingerprint". The hash enables the blockchain to store files of arbitrary size efficiently by using a small and unique hash value. Because any change to a file would result in a different hash, users can prove the validity of a file by computing the hash and comparing that hash with the hash stored on chain.

Build a custom pallet

The Substrate node template has a FRAME-based runtime. As you learned, FRAME is a library of code that allows you to build a Substrate runtime by composing modules called pallets. You can think of the pallets as individual pieces of logic that define what your blockchain can do. Substrate provides you with a number of pre-built pallets for use in FRAME-based runtimes.

This tutorial demonstrates how to create your own FRAME pallet to be included in your custom blockchain.

Before you begin

1. Make sure you already have Rust for Substrate setup on your computer:

   https://docs.substrate.io/install/

2. Clone the substrate-node-template.

   git clone https://github.com/substrate-developer-hub/substrate-node-template

3. Replace the contents of substrate-node-template/pallets/template/src/lib.rs with:

   Note: This code will not compile until you complete the full tutorial. The goal is to show you the skeleton of a pallet, and fill in all the parts piece by piece.

   #![cfg_attr(not(feature = "std"), no_std)]
   
   // Re-export pallet items so that they can be accessed from the crate namespace.
   pub use pallet::*;
   
   #[frame_support::pallet]
   pub mod pallet {
   	use super::*;
   	use frame_support::pallet_prelude::*;
   	use frame_system::pallet_prelude::*;
   
   	#[pallet::pallet]
   	pub struct Pallet<T>(_);
   
   	#[pallet::config]  // <-- Step 2. code block will replace this.
   	#[pallet::event]   // <-- Step 3. code block will replace this.
   	#[pallet::error]   // <-- Step 4. code block will replace this.
   	#[pallet::storage] // <-- Step 5. code block will replace this.
   	#[pallet::call]    // <-- Step 6. code block will replace this.
   }